Given the delay it seems like everyone is waiting for someone else -- I'm going to press ahead with Var's action.
I'll take the narrow ledge, is it narrow enough to require rolls? If so I'll see if anyone has rope to tie around me and someone relatively strong to reel me back out of the water if I fall.
Tying a rope around his waist, Var hands the rest to Wallace and begins to edge his way out into the river tunnel, working his feet carefully to find purchase on the narrow ledge.
Spoiler: Acrobatics/Balance check show
The ledge is uneven, but over 12" wide, but it is slippery from the mist and spay. I'll say a DC 15 Acrobatics/Balance check (success = move up to 1/2 speed, per p.69)1d20+5=14
Var moves 5' along the ledge -- it's slow going and even with his Skinwalker's Cape helping him see in the faint light, Var can't seem to shake the thought of being whisked away into the uncertain darkness of the underground river.
Even with the limited light, Var, getting a better look at the river tunnel is certain that while the area near the former arch has a higher ceiling as part of a natural cavern structure, the river tunnel continues on its own further, with a gradually descending ceiling within Var's sight range.